Oral-recombinant Methioninase in Combination With Rapamycin Eradicates Osteosarcoma of the Breast in a Patient-derived Orthotopic Xenograft Mouse Model.

BACKGROUND/AIM: Primary osteosarcoma of the breast is a very rare malignancy that shares histological features with osteosarcoma. It is also highly sensitive to methionine restriction due to methionine addiction. We previously established a patient-derived orthotopic xenograft (PDOX) nude-mouse model derived from tumor tissue of a patient with primary mammary osteosarcoma. In the present study, we investigated the efficacy of oral-recombinant methioninase (o-rMETase), combined with rapamycin, an inhibitor of mammalian target of rapamycin (mTOR) kinase, on a mammary osteosarcoma PDOX nude-mouse model. MATERIALS AND METHODS: The PDOX mouse model was established by surgically transplanting a specimen of primary osteosarcoma of the breast into the mammary gland of nude mice. Mice implanted with tumors were randomly divided into four groups: Control group, N=5; rapamycin-treated group, N=5; o-rMETase-treated group, N=5; and a group treated with the combination of o-rMETase and rapamycin, N=5. Mice were treated for 2 weeks after transplantation, and tumor volume was measured during the treatment period. RESULTS: Treatment with the combination of rapamycin and o-rMETase eradicated the osteosarcoma of the breast compared to the untreated control (p=0.000008). o-rMETase alone did not significantly inhibit tumor growth, and rapamycin alone only partially inhibited the tumor (p=0.78 and p=0.018, respectively) compared to the untreated control. There was not a significant difference in mouse weight between the groups. CONCLUSION: The combination of rapamycin and o-rMETase was highly effective against primary osteosarcoma of the breast in a PDOX model, suggesting a future clinical strategy for this rare cancer type that currently has no first-line treatment.

Oral-recombinant Methioninase Lowers the Effective Dose and Eliminates Toxicity of Cisplatinum for Primary Osteosarcoma of the Mammary Gland in a Patient-derived Orthotopic Xenograft Mouse Model.

BACKGROUND/AIM: Primary osteosarcoma of the mammary gland is a very rare disease, accounting for under 1% of all mammary gland malignancies. There is no established first-line treatment, and prognosis is poor compared to conventional breast cancer. We previously demonstrated the efficacy of cisplatinum and eribulin in a patient-derived orthotopic xenograft (PDOX) mouse model of primary breast osteosarcoma. However, these drugs show significant clinical toxicity. All cancers are addicted to methionine (Hoffman effect). In the present study, we determined whether methionine restriction with oral recombinant methioninase (o-rMETase) would lower the effective dose of cisplatinum in a PDOX model of primary osteosarcoma of the mammary gland, thereby reducing its toxicity. MATERIALS AND METHODS: Mouse PDOX models of primary osteosarcoma of the breast were randomized into the following groups: control; cisplatinum (weekly at 3 or 6 mg/kg); twice-daily o-rMETase; or o-rMETase combined with 3 mg/kg cisplatinum, with treatment for 2 weeks. RESULTS: Cisplatinum at 6 mg/kg significantly inhibited breast osteosarcoma growth compared with the untreated control and mice treated with 3 mg/kg cisplatinum (p=0.01 and 0.009, respectively). There was no significant difference in tumor growth between mice treated with cisplatinum at 3 mg/kg and the control (p=0.16). Combination therapy with cisplatinum at 3 mg/kg and twice daily o-rMETase regressed the osteosarcoma of the mammary gland (p=0.009), similar to the inhibition by cisplatinum at 6 mg/kg alone. Cisplatinum at 6 mg/kg caused a significant loss of mouse body weight, compared to the control (p=0.02). There was no significant body-weight loss with the combination therapy of o-rMETase and cisplatinum at 3 mg/kg, compared to the untreated control. CONCLUSION: o-rMETase halved the effective dose of cisplatinum, thereby eliminating cisplatinum toxicity, demonstrating a future clinical strategy for therapy of osteosarcoma of the breast.

The First Mouse Model of Meckel's Diverticulum Carcinoma.

BACKGROUND: Cancer of the Meckel's diverticulum (MD) is extremely rare. It is often advanced at the time of operation and the prognosis is poor. An effective treatment for this cancer has not yet been developed and there is no MD-carcinoma mouse model. MATERIALS AND METHODS: MD carcinoma was established as a patient-derived xenograft (PDX) in 5-week-old male nude mice by subcutaneous transplantation of surgical specimens together with surrounding normal tissue. Hematoxylin and eosin (H&E) staining was performed on paraffin-embedded tissue sections of the original tumor resected from patients and transplanted tumors grown in nude mice. RESULTS: Three of five mice implanted with MD tumor fragments grew. MD-carcinoma histopathology, observed with H&E-stained tissue sections of the tumors grown in the mice and tumor from the original patient, was concordant. Both showed the luminal structures characteristic of MD carcinoma, and the lumens were filled with serous fluid. CONCLUSION: The first PDX mouse model of MD carcinoma has been established. The PDX model maintained MD-carcinoma histology of the tumor in the patient. The MD carcinoma mouse model will enable basic research on MD carcinoma, as well as the testing of novel therapeutic agents.

The Combination of Cisplatinum and Doxorubicin Regressed Primary Osteosarcoma of the Breast in a PDOX Mouse Model.

BACKGROUND/AIM: Primary osteosarcoma of the breast is an exceedingly-rare malignant tumor that shares histological characteristics with osteosarcoma of the bone. Since effective therapies have not yet been established, standard therapy for osteosarcoma of the bone was examined in the present study for efficacy against primary osteosarcoma of the breast in a patient-derived orthotopic xenograft (PDOX) nude-mouse model. MATERIALS AND METHODS: The PDOX mouse models were established by surgical implantation of the primary osteosarcoma of the breast specimen into the mammary gland of nude mice. Mice with tumors were randomized into four groups, each n=4: control group; cisplatinum (CDDP)-treatment group; doxorubicin (DOX)-treatment group; and CDDP/DOX-combination-treatment group. Mice were treated for twenty-one days, three weeks after implantation. Tumor size and body weight were measured during three weeks of treatment. RESULTS: Significant tumor growth inhibition was observed, compared to the control, in the CDDP-treatment group, the DOX-treatment group, and the combination-treatment-group. Only the combination treatment regressed the tumor. CONCLUSION: CDDP and DOX which are standard first-line therapies for osteosarcoma, may be clinically effective against primary osteosarcoma of the breast, and in particular, their combination.